Conventionally, among various types of semiconductor devices, IPM (Intelligent Power Module) semiconductor devices are used in electric power source control. These semiconductor devices, often used to control a large amount of electrical power and tending to generate heat, include a plurality of semiconductor chips, a plurality of die pads, a metal layer serving as a heatsink, a junction layer and a sealing resin. Each of the semiconductor chips is disposed on one of the die pads. Each die pad is joined to the metal layer by the junction layer. The sealing resin covers the semiconductor chips, the die pads, the heatsink and the junction layer. A semiconductor device so called IPM is disclosed in Patent Document 1 for example.
Such a semiconductor device is mounted on a substrate (circuit substrate). Under this state where the semiconductor device is mounted on a substrate, the heatsink is faced to a relatively large heat releasing member outside of the semiconductor device. If, however, the junction layer has a portion extending out of the sealing resin, a gap may be made between the metal layer and the heat releasing member. This prevents efficient transfer of heat from the semiconductor chips to the heat releasing member.
The heat releasing layer and the sealing resin are made of different materials. Due to this, the outer edge of the heat releasing layer may come off the sealing resin. If this separation grows along the sealing resin, heat release from the semiconductor chips may be hindered and/or the semiconductor chips may be corroded.
When bonding aluminum wires, pressure and vibration are applied to the wires. The pressure and vibration are further applied to the die pads and the wire bonding regions. If the die pads and/or the wire bonding regions vibrate or deform, however, the bonding of the wires cannot be performed properly.
As noted above, a conventional semiconductor device may be mounted on a substrate (circuit substrate), and in the substrate-mounted state, the heatsink is faced to a relatively large heat releasing member outside of the semiconductor device. Also, a plurality of semiconductor chips are mounted on the die pads via solder paste, and in addition, thick and hardwires made of aluminum, for example, are used to provide electrical connection between each semiconductor chip with a lead so that a large amount of electric current can pass through.
In the above-noted semiconductor device, when a plurality of semiconductor chips are mounted, adjacent semiconductor chips may be unduly connected to each other via solder paste. Also, there can be a problem of so called solder erosion in which only part of the solder paste reaches an end of the die pad. Further, there is another problem that surface tension, for example, in the solder paste can move the semiconductor chips out of their predetermined positions. Such a shift of the semiconductor chips from their predetermined positions sometimes makes it difficult to bond them with hard wires. If the semiconductor chips are spaced from each other at an increased distance in order to avoid this problem, then there is another problem that the overall size of the semiconductor device is increased.